Electrodepostion of metal from alkaline cyanide bath



Patented Oct. 6, 1953 V UNITED STATES PATENT OFFICE ELECTRODEPOSITION OF METAL FROM CYANIDE BATH Herbert K. De, Long, Midland, Mich., assignor' to The Dow Chemical Company, Midland, Mich;, a. corporation ofDel'aware No Drawing. Application September 3, .1948, Serial No. 47,745

8 Claims. (Cl. 20446) 1 2 The invention relates to improvements in the Example 111 art of electroplating metal, particularly the electrodeposition of copper, silver and gold in aquegggggf ii' f g' 26 25 1 ous alkaline cyanide plating baths. sodium cyanide I have discovered that inorganic. fluorides, 5 Sodium carbonai especially the alkali metal and ammonium flu- Ammonium g 'd 1 orides, exert a marked beneficial efiect on, the. Temperature electrodeposited plates of copper, silver and gold pH 5 to 11 0 when present in substantial amount in the conventional aqueous alkaline cyanide plating baths 1O Cathode current of these metals. One of the. principal advantages Example ]V which results from the use of the inorganic flusilverplatmg bath: oride in accordance with the invention is in in"- sil cyanide 9 1 creasing the brightness of the, deposit. Another Potassium cya'dmdm advantage is the reduction of pitting or immer- Potassium LII sion corrosion. These advantages obtain more Potassium especially in the plating of magnesium and its. Temperature 04 0 E alloys, particularly when first coated with zinc pH 0 51:0 2 0 by the immersion coating process described in I my copending application Serial No. 778,283, filed 2o Cathode current densltyfl amp/Sq October 6, 1947, now U. s. Patent 2,526,544. Example The fluorides I prefer to use are either potassilver plating bath; sium fluoride (KF) or ammonium bifiuQrid silver cyanide 24 g p 1 (NI-RF-HF) and'amounts in the order of about 5 sodium cyanide to 100 grams per liter of plating solution may be 25 Potassiumn'itrate 1125 used. Preferred concentrations are in the range Potassium fluoride of about 20 to 60 grams per liter. In the follow- Temperature 7 t R ing tabulations examples of plating baths compI-I- 105 pounded in accordance with the invention are set th d current density 20 amp/sq. it. forth, together with appropriate operating con- 30 ditions. Example" VI Example I Gold plating bath: Potassium gold cyanide--- 3.75 g. p. 1. Copper platmg j Potassium carbonate 7.5., Coppel: Potassium cyanide 3.75, Ptasslum cyan-me Potassium fluoride so. Rochel'le Temperature -80-F'. Potassium fiuonde-.. 60. 0 DH gg ig Cathode current density 5-15 amp./sq.,ft. Cathode current density 15 amp/sq. ft. 40 In the foregoing eXampleS e platin b th compositions, except for the fluoride constituent, Emmple H are conventional. It will be understood that Copper plating bath: these examples are illustrative and are not to be Copper cyanide g. p. l. 45 taken as limitative of the invention. The essen- Sodium cyanide 135. tial requirements of the plating baths are the Potassium hydroxide 42. presence as the cyanide in water solution of the Sodium thiocyanate 15. metal to be deposited, together with sufiicient Betaine 1.5. alkalinity to maintain the pH in the range of Potassium fluoride 60. 50 about 9 to 13, and, in accordance with the in- Temperature to F. vention, the fluoride constituent is included. pH 12.5 to 13.5. Insofar as the pH is concerned it is preferable to Cathode current density 15 amp./sq.ft. operate the copper plating baths at a pH between about 10 and 13 and the silver and gold baths at a pH between about 9 and 12. This alkalinity is readily obtained by the addition to the plating bath of an alkali metal hydroxide or carbonate such as NaOH, KOH, KzCOs and NazCOa or ammonium hydroxide. The presence of free cyanide (ON) in addition to that furnished by the cyanide of the metal to be deposited is desirable. This may be supplied by including in the bath an alkali metal cyanide such as sodium cyanide and potassium cyanide in amount such as to yield from about 2 to grams of CN per liter.

In plating magnesium and its alloys in aqueous alkaline cyanide baths containing fluoride in accordance with the invention, it is advantageous first to deposit a film of zinc upon the Work as described in my patent application aforementioned. This may be accomplished, for example, by immersing for 5 minutes the article to be plated in the following Zinc immersion coating bath:

Na4PzO7 grams 10.0 ZIISO4'7H2O dO 4.0 KB do 1.0 K2CO3 C 0.5 Water 'sufiicient to make 100 grams of solution pH of solution About 10.2

Copper strike bath: G. p. 1. Copper cyanide 41.3 Sodium cyanide n 50.8 Sodium carbonate 30 Rochelle salts 45 Sodium thiosulphate l 1.9

(pl-I about 10 to 11.)

Cathode current density 5 to 10 amp/sq. ft. for 2 to 3 minutes followed by an increase of current density to amp/sq. ft. for about 3 minutes.

The presence of the soluble fluoride in the alkaline cyanide plating bath has the advantage of reducing or preventing immersion deposition and attack upon the work. Attack is sometimes revealed by the presence of a smutty film on the work and the formation of pits. The electrobath maintained at about 4 plates obtained in the presence of the fluoride are brighter, and pitting of the work due to corrosion by the bath is overcome.

I claim:

1. In a method of depositing an electroplate of a metal selected from the group consisting of copper, silver, and gold upon articles of ma nesium and magnesium alloys from an aqueous alkaline cyanide plating solution having a pH of 9 to 13 and containing a cyanide of one of the metals selected from the group consisting of copper, silver, and gold and from 2 to 5 grams per liter of CN provided by an alkali metal cyanide by electrolyzing the solution with the article as cathode whereby the selected metal is electrodeposited on the article, the improvement which consists in dissolving in the plating solution a Water-soluble inorganic fluoride selected from the group consisting of the alkali metal and ammonium fluorides in amount from 5 to grams per liter of the plating solution.

2. The method according to claim 1 in which the water-soluble inorganic fluoride is ammonium fluoride.

3. The method according to claim 1 in which the water-soluble inorganic fluoride is an alkali metal fluoride and the metal to be deposited as an electroplate is copper.

4. The method according to claim 1 in which the water-soluble inorganic fluoride is an alkali metal fluoride and the metal to be deposited as an electroplate is silver.

5. The method according to claim 1 in which the water-soluble inorganic fluoride is an alkali metal fluoride and the metal to be deposited as an electroplate is gold.

6. The method according to claim 1 in which the water-soluble inorganic fluoride is ammonium fluoride and the metal to be deposited as an electroplate is copper.

7. The method according to claim 1 in which the water-soluble inorganic fluoride is ammonium fluoride and the metal to be deposited as a electroplate is silver.

8. The method according to claim 1 in which the water-soluble inorganic fluoride is ammonium fluoride and the metal to be deposited as an electroplate is gold.

HERBERT K. DE LONG.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 946,903 Kern Jan. 18, 1910 2,449,726 Slatkin Sept. 21, 1948 OTHER REFERENCES 

1. IN A METHOD OF DEPOSITING AN ELECTROPLATE OF A METAL SELECTED FROM THE GROUP CONSISTING OF COPPER, SILVER, AND GOLD UPON ARTICLES OF MAGNESIUM AND MAGNESIUM ALLOYS FROM AN AQUEOUS ALKALINE CYANIDE PLATING SOLUTION HAVING A PH OF 9 TO 13 AND CONTAINING A CYANIDE OF ONE OF THE METALS SELECTED FROM THE GROUP CONSISTING OF COPPER, SILVER, AND GOLD AND FROM 2 TO 5 GRAMS PER LITER OF CN PROVIDED BY AN ALKALI METAL CYANIDE BY ELECTROLYZING THE SOLUTION WITH THE ARTICLE AS CATHODE WHEREBY THE SELECTED METAL IS ELECRODEPOSITED ON THE ARTICLE, THE IMPROVEMENT WHICH CONSISTS IN DISSOLVING IN THE PLATING SOLUTION A WATER-SOLUBLE INORGANIC FLUORIDE SELECTED FROM THE GROUP CONSISTING OF THE ALKALI METAL AND AMMONIUM FLUORIDES IN AMOUNT FROM 5 TO 100 GRAMS PER LITER OF THE PLATING SOLUTION. 